Floating roof tanks are widely used for storing volatile petroleum-based liquids. The floating roof of this type of tank has a built-in buoyancy which allows it to float on top of the liquid product contained in the tank. Floating roof tanks may be configured either as internal floating-roof tanks or as external floating-roof tanks. In each configuration, the floating roof is designed to remain in contact with the liquid surface of the product and to cover all of the surface of the product except for a small annular surface area between the outermost rim of the floating roof and the inside surface of the tank shell. In other words, the overall diameter of the roof has a diameter which is smaller than the inside diameter of the tank, leaving a gap between the circumferential edge of the roof and the inside diameter of the tank. To prevent the release of volatilized product from the tank as well as preventing rain water from entering the tank, this gap is closed or sealed by a flexible sealing system, which retains the seal as the roof is raised and lowered by the level of the product within the tank.
The primary objectives of the prior art typically address improving the sealing arrangement for floating roof tanks, as acknowledged in U.S. Pat. No. 4,308,968 by Thiltgen, et al. The '968 patent discloses the benefits of having a secondary seal which is highly flexible and capable of conforming to changing shapes and sizes of the surrounding walls and parts and which also protects the vapor-impermeable portions of the seal against rapid wear and deterioration.
The environmental benefits of floating roof tanks are widely disclosed, and regulations which severely restrict the release of volatile organic compounds into the atmosphere are ubiquitous. For permanent facilities, the known floating roof tanks provide a good solution for containing the release of these volatile emissions. However, heretofore, the control of volatile emissions from temporary storage facilities, such as temporary test tanks, has been problematic, often requiring extensive vapor recovery systems capable of handling the large volumes of the volatile emissions. One means of mitigating this problem would be a transportable floating roof tank. However, floating roof tanks are generally designed for large permanent facilities. The issue is not of size, because a smaller tank can always be fabricated to facilitate transportation, but rather whether the tank will withstand the various dynamic loads to which it will be subjected in the course of being transported and placed. There is the issue of the structural integrity of the tank itself, and there is also the issue of protecting the integrity of the primary and secondary seals between the floating roof and the inner wall of the tank.
In order for a tank to be portable, the tank must have a structural integrity which will withstand the various forces to which the tank will be subjected during the course of lifting and transporting. Recently, portable vertical tanks which are capable of withstanding the dynamic loads the tank experiences in the course of transportation and placement have been developed. However, when such tanks are equipped with a floating roof, protecting the integrity of the seals for transportation of the portable vertical tank is not known in the art. Any seal elements between the floating roof and the inner tank wall will be subjected to the weight of the floating roof and connected structures if the position of the tank is changed from a general vertical operating position to a horizontal position for transportation and/or storage. Thus, changing the position of a floating roof tank to a horizontal orientation as generally required for transportation will result in the crushing of the seals causing damage the integrity of the seals.